1. Field of the Invention
This invention pertains generally to voltage controlled oscillators (VCOs), and more particularly to submillimeter wave VCOs.
2. Description of Related Art
Voltage controlled oscillators (VCOs) are key components in a variety of sensor, imaging and communication applications. Much ongoing interest has been focused on the submillimeter wave regime and the ability to generate controllable frequencies toward the Terahertz range (300 GHz to 3 THz), such as for implementing communication systems as well as high resolution sensors and imaging devices. Moving toward shorter submillimeter wavelengths of course increases communication bandwidth. In addition, the submillimeter wave regime can provide a host of sensor and imaging devices which are capable of seeing through materials such as fog and clothing, and can provide a means of readily detecting concealed objects.
Currently, practical (e.g., low cost and/or readily implemented) submillimeter wave approaches extend up to about 190 GHz, above which gain losses, efficiency losses, and increased phase noise renders them unsuitable for practical applications. These current practical approaches are unable to reach beyond the 190 GHz range and into those portions of the spectrum within which less signal attenuation is encountered.
In addition, attempts toward reaching the submillimeter wave regime have typically required the use of exotic materials and processes which are incompatible with integrated circuit fabrication. However, operation at submillimeter wavelengths is currently not attainable with low cost practical circuits, but requires the use of exotic material and techniques, for example free-electron radiation, optical lasers, Gunn diodes or fundamental oscillation by using III-V based HBT/HEMT technology.
Therefore, a need exists for methods and apparatus for fabricating practical submillimeter wave VCOs which reach beyond 190 GHz with sufficient gain and efficiency and while minimizing phase noise. The present invention addresses that need and overcomes shortcomings of existing approaches.